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I've decided to close the site at the end of the year. I appreciate all that have contributed to funding the site over the years. Ad revenue used to supplement the cost. Ad revenue has dropped significantly. It is just too costly to keep it running and I need to simplify things. I don't have time to move the site to a cheaper host. Not even sure it would work since the forum software is old and may not work on current versions of php. The site is plus 15 years old. Not a bad run in internet years.

First a little history. I bought this car (1998 318ti) about 4 years ago. At that time, I replaced all the hoses, radiator, water pump, thermostat, cooling fan, fan switch, plastic connectors on the motor. The car run fine for a year or so until I was in a traffic tie up on a hot night. Long story short, the plastic connector to the heater core broke causing the motor to overheat. Removed the head, had it cut and the valves done. Reassembled the motor with the correct head gasket from BWW, and found there was no compression on #4 cylinder. Removed the head only to one of the lifters was stuck. (Add new lifters and another head gasket to the above list)

I worked through those issues and have the car running but now I find that it overheats. Using an aftermarket OBD temperature gauge, it will go past 250f (I shut it down at that point) Radiator bled while front of car was as high as my floor jack would go. Heater blows hot air, but the bottom radiator hose stays cool. Turning the heater fan on high will cool the motor for a few minutes then it goes back up. Not leaking any antifreeze.

All that seems to point at a thermostat stuck closed. I removed the thermostat and dropped in boiling water. Nothing happened. I received a new BWM t-stat today and decided to test first. Same thing, nothing happens.

Shouldnít I be seeing the t-stat open? Both bad?

Any other thoughts on what could be going on?

I donít want to give up on this car. The body and interior are mint. Iíve a ton of money into replacement parts. I'm just tired of throwing money at it and not being able to drive.

I spent some time on youtube this morning looking for videos that showed t-stat tests. Although I did not find an m44 test, I did find others that showed definite movement. Next, I took some measurements from the t-stat and the head. They showed the front disk would have to move almost ľ inch to close off the port.

My experience is that these thermostats get stuck open. I bought two cars with that going on. I've used the Behr and haven't had any issues.

Possibly you can hack the thermostat part out of the old housing to test without thermos bit? Never really looked at it closely.

Will be interesting to see what you find. Maybe a weak water pump?

I've had two fail, both stuck open. Failed during the summer, didn't even know it. Weather turned cold, car wouldn't heat up fully. The thermostat element is removable from the housing, just twist. I've spent hours researching the part, looking through catalogs online, and talking to tech support at various mfg - nobody offers the thermostat element separate from the housing, which of course makes a $10 part a $50 part. Hmm...maybe the thermostatic element could be removed from the housing and run the car that way - that would provide another data point.

I had already tried removing the inners of the t-stat. That made no difference. After a lot of searching on google I found the reason why. The port in the head has to be closed to allow water to move into the radiator. If not closed, the water just circulates though the block.

The pump is a Stewart with the metal impeller. That was replaced when I bought the car. While that’s been 4 years, the car has been sitting most of the time. It gets discouraging when you put something back together using the best parts available only to find it still can’t be driven.

I’ve own a few e30’s and found them to be rock solid dependable cars. This ti has been a learning experience. -------------------------------------- Paul, From what I understand, if they fail open the only problem would be as you describe.

There is a small hole in the in the disk that is closest to the thermostat side but it is has some type of one-way valve. Vent to let trapped air out?

The new t-stat came today. A behr packaged in a box labeled Vernet. It seems I paid extra for the box, not happy about that.

I did test the new t-sat and found the best way was dip into boiling water. Then lift out and tip up the end that goes to the bottom hose. You should be able to see the water trapped flow past the disk. I had tested the other one the same way but at the time I wasn’t sure what I was looking for.

I’m not sure at what point it fully opens but it must be over 212f as it was hard to notice the outer disk moving. This is in line with Paul’s post stating the movement is pretty subtle.